Dampener for lithographic printing



2,395,654 DENER' son mnocnarmc ramma Thomas Peter Brannigan, Gordon Harold liaison; and William Henry Yoder, Detroit, Micln, as-

signors to General Motors Corporation, Detroit, Micln, a corporation of Delaware No Drawing. Application June 30, 1941, 4 Serial No.400,568 I 13 Claims. (cams-2) This. invention relates to dampening fluid for lithograph'plates and stones. Lithograph plates or stones for printing are prepared by throwing light througha'photographic negative onto a film of sensitized albumen. The light insolubilizes the portions of the colloid albumen.

of a screen. The size of the dots determinesthe shading. a

A deep form of lithography is described and claimed in the Grass Patent No. 1,155,342 in which a positive is used and the light passed through onto a'sensitized film of albumen and the portions of the plate bearing the image are slightly etched by a suitable etching fluid. The etched' portions are filled with nitrocellulose varnish which serves to hold the ink.

Wood graining on metal is usually done by the photogravure process described and claimed in the Henry Patent No. 1,548,465. In the photogravure process the image is formed by cells in the copper plates of more or less depth,.

depending upon the tone, the darker the image the deeper the cell and more ink that will be poured on. The printing, of course, is not done directly 'from a metal plate or roll onto the metal to be grained, but is done by a transfer roll of gelatin or rubber.

Ofl'set printing by lithograph has also here tofore been used for graining metal. However,

it has been usual to use a number of color plates, that is, separate impressions are made for each color desired in the final work. Consequently, several photographs are taken through color screens; one for each color and separate plates or stones are made for each color.

In lithography the grease or varnish catches image and the-blank portions, This solution is made of: I

Water gallons 1 Aerosol cubic centimeters 5 Ammonium dichromate grams-.. 40

Gum arabic--.. "ounces" 2 Potassium dichromate or sodium dichromate may be substituted for ammonium dichromate.

The dichromate acts as a mild etching fluid for keeping the-plate clean and this sometimes eats into the plate. The gum arabic fills in the 'plate so roughened and keeps it smooth and water absorbent. The Aerosol is a commercial wetting agent made by the American Cyanamld & Chemical Corporation. Commercial wetting agents are now on the market and there are. several of these which may be-purchasedand will probably do equally, or nearly as well as the aerosol. Aerosol comes in four groups; the 0. 23. group,

which isdeflned as the alhtl aryl sulphonate,f--

and the 0,. T., N. A. and A.-'Y. groups are sulphonated esters of dicarboxylic acid. The

point is to provide a wetting fluid of; great penetrability. This serves to cause the dampening fluid to readily spread and immediately reach clear to the margin of the image, whether it be a grease or cellulose varnish. The wetting fluid is a fluid that has very little-or no surface tensio'n. When the wetting fluid does not reach right up to the body of the image, then the ink will often spread slightly onto the portions of the plate adjacent the image and give a blurred We appreciate-that dichromate such as potassium dichromate. and gum arable and water i. have been used-in dampening compounds, but

and holds the ink and the rest oithe plate is dampened with water by first rolling the plate with a wet roll. We have found that with ordinary wetting or dampening solutions the line of demarcation between the greased or varnished image portions and the wet portions of the plate that are to repel the-ink, are not clear cut enoughto produce satisfactory results in graining. We have found adampening liquid which we believe is superior for wetting the blank portions of the stone or plate and which aflords a- I mild etching fluid, a wetting agent havingllttle much cleaner line of demarcation between the so far as we know, these have never been com- "bined from a wetting agent such as aerosol or its equivalents. 1

What we claim is: i

1. A damnefier for lithographic printing; or graining which comprises, a solutionoi water. ammonium dichromate, gum 'arabic and a wetting agent having. penetrabllityf relatively" greater than water.

"2. A dampener for lithographic printing or graining which comprises a solution of water, an alkaline dichromate and a wetting agent havins. relatively great penetrability.

3. A dampener for lithographic printing or graining which'comprises water, a: solution of a surface tension and gum arabic. 4. A dampener for lithographic printing or graining which; comprises a solution of water, a wetting agent havingrelatively great penetrability and a mild etching fluid. g

5. A dampener for lithographic printing or graining which comprises a solution of water and a wetting agent selected from the group which consists of alkyl aryl sulphonates and theesters of sulphonated dicarboxylic acid.

6. A dampener for lithographic printing or graining which comprises a solution of substantially one gallon of water, five cubic centimeters of a wetting agent having relatively great penetrability, forty grams of a mild etching fluid and two ounces of gum arabic.

r '7. A dampener for lithographic printing or graining which comprises a solution of substantially one gallon of water, five cubic centimeters of alow surface tension liquid, forty grams of ammonium dichromate and two ounces of gum arabic.

8. A step in lithographic printing or graining which comprises wetting the lithographic printing plate or stone with a solution of water, ammonium dichromate, gum arabic and a wetting agent having relatively great penetrability.

9. A step in lithographic printing or graining which comprises wetting the lithographic printing plate or stone with a solution of substantially one gallon of water, five cubic centimeters of a wetting agent having a. relatively low surface tension, forty grams of ammonium dichromate and two ounces of gum arablew 10. A step in lithographic printing or graining which comprises wetting the lithographic printing surface with a solution of water, an etching fluid selected from the group consisting of potassium, ammonium and sodium dichromates, a

wetting agent selected from the group consisting ;of alkyl aryl sulphonates and sulphonated esters of dicarboxylic acid.

11. A step in lithographic printing or graining which comprises wetting thelithographic printing surface with a solution of water, an etching fluid selected from the group consisting of potassium, ammonium and sodium dichromates, a wetting agent selected from the group consisting of alkyl aryl sulphonates, sulphonated esters of dicarboxyiic acid and gum arabic.

12. A step in lithographic printing or graining which comprises wetting the lithographic printing surface with a solution of substantially one gallon of water, substantially forty grams of an etching fluid selected from the group consisting of potassium, ammonium and sodium dichromates, substantially five cubic centimeters of a wetting agent selected from the group consisting of alkyl aryl sulphonates and sulphonated esters of dicarboxylic acid.

13. A step in lithographic printing or graining which comprises wetting the lithographic printing surface with a solution of substantially one gallon of water, substantially forty grams of an etching fluid selected from the group consisting of potassium, ammonium and sodium dichromates, substantially five cubic centimeters of a wetting agent selected from the group consisting of alkyl aryl sulphonates, sulphonated esters of dicarboxylic acid and substantially two ounces of gum arable.

' THOMAS PETER BRANNIGAN.

GORDON HAROLD RAISON. WILLIAM I-ENRY YODER. 

